# Talk:Nonlinear finite elements/Nonlinear axially loaded bar

I think the second last equation is wrong, or at least I don't see how ${\displaystyle \left(\sum _{j}u_{j}{\cfrac {dN_{j}}{dx}}\right)^{2}=\sum _{j}u_{j}\left({\cfrac {dN_{j}}{dx}}\right)^{2}}$
I had the same thought after reading it. There should remain terms with ${\displaystyle u_{j}}$ squared, which makes it not possible anymore to write the DE as a matrix problem. This makes sense to me, since it is a nonlinear DE in the first place. I think it is wrong and should be corrected/removed. --141.135.57.121 (discuss) 23:33, 10 September 2014 (UTC)